Potential dead horse: how bad is FF's deep DoF disadvantage?

DoF is entirely a product of the aperture diameter. So a 24mm F4 will have the same DoF as 48mm F8, 12mm F2 etc etc.

For the same focal distance, display size, viewing distance, and visual acuity, yes.

As someone explained to me in another thread, for equivalent photos this phenomenon cancels out larger formats' high ISO advantage for completely equivalent pictures. For example to maintain shutter speeds, that 24mm F4 on an FF camera will need to be shot at 2 ISO stops higher than 12mm F2 on an MFT camera. At which point the noise on the FF is at best the same but in some cases worse if we are talking very high ISOs.

Correct. Equivalent photos (same DOF and shutter speed) are made from the same total amount of light, so the noise advantage will go to the system with the more efficient sensor.

However, this noise differential due to differences in sensor efficiency can be extended or closed based on how detailed the photo is. That is, the system that resolves more detail can make greater use of NR (noise reduction).

So my question is, for folks who have used an array of different formats extensively, how much does this affect real world shooting? Did you ever find yourself frustrated with the inability to get deep DoF from larger formats, or is it not that big of a deal?

It would depend heavily on the particular bodies being compared and the ISO being used. This post has some very interesting comparisons between FF and mFT based on the particular ISOs being used:

It seems to me more and more like no format is superior to another... they all have advantages and disadvantages that make them better for different kinds of photography, with no clear all around winner

One would take that as a given, I should think. In my personal opinion, differences between systems based on operation, size, weight, and price matter way, way, way more than differences based on IQ and DOF control for the vast majority.

Most people will ignore DoF issues and then larger sensors will have the IQ advantage. This thing about strict "equivalence" is just a technical correct thing that has very little application. Except for FL equivalence, everything else is mostly irrelevant.

And, if one wants to bring DoF into the picture, many will like to have the ability to isolate a subject using a shallow focus range, very used in portraiture, PJ, sports, and so on.